Add streaming parameter files

README.md

@@ -87,6 +87,15 @@ option:
 hyperfine -L compiler gcc,clang '{compiler} -O2 main.cpp'
 ```
 
+For large parameter sets, values can be read one line at a time from a file with
+`--parameter-file`:
+
+```
+hyperfine --parameter-file compiler compilers.txt '{compiler} -O2 main.cpp'
+```
+Both LF and CRLF line endings are supported. The file is processed with a buffered reader, so its
+full contents are not held in memory.
+
 ### Intermediate shell
 
 By default, commands are executed using a predefined shell (`/bin/sh` on Unix, `cmd.exe` on Windows).

src/benchmark/scheduler.rs

@@ -46,14 +46,25 @@ impl<'a> Scheduler<'a> {
 
         executor.calibrate()?;
 
-        for (number, cmd) in reference.iter().chain(self.commands.iter()).enumerate() {
-            self.results
-                .push(Benchmark::new(number, cmd, self.options, &*executor).run()?);
+        let mut number = 0;
+        let results = &mut self.results;
+        let options = self.options;
+        let export_manager = self.export_manager;
+        let mut run_command = |cmd: &Command<'a>| -> Result<()> {
+            results.push(Benchmark::new(number, cmd, options, &*executor).run()?);
 
             // We export results after each individual benchmark, because
             // we would risk losing them if a later benchmark fails.
-            self.export_manager.write_results(&self.results, true)?;
+            export_manager.write_results(results, true)?;
+            number += 1;
+
+            Ok(())
+        };
+
+        if let Some(reference) = reference.as_ref() {
+            run_command(reference)?;
         }
+        self.commands.try_for_each(run_command)?;
 
         Ok(())
     }

src/cli.rs

@@ -200,6 +200,26 @@ fn build_command() -> Command {
                      possible parameter combinations.\n"
                 ),
         )
+        .arg(
+            Arg::new("parameter-file")
+                .long("parameter-file")
+                .action(ArgAction::Set)
+                .allow_hyphen_values(true)
+                .value_names(["VAR", "FILE"])
+                .conflicts_with_all([
+                    "parameter-scan",
+                    "parameter-step-size",
+                    "parameter-list",
+                ])
+                .help(
+                    "Perform benchmark runs for each line in FILE. Replaces the string '{VAR}' \
+                     in each command by the current line. FILE is processed line by line, so its \
+                     full contents are not held in memory.\n\n  Example:  hyperfine \
+                     --parameter-file compiler compilers.txt '{compiler} -O2 main.cpp'\n\nThis \
+                     performs benchmarks for 'gcc -O2 main.cpp' and 'clang -O2 main.cpp' if FILE \
+                     contains the lines 'gcc' and 'clang'.",
+                ),
+        )
         .arg(
             Arg::new("shell")
                 .long("shell")